The present invention relates to a steering shaft assembly for automotive vehicles, and more particularly to a steering shaft assembly of the telescopic type adjustable in its axial direction.
A conventional steering shaft assembly of the telescopic type as described above comprises an upper shaft mounted thereon with a steering wheel, a lower shaft telescopically connected to the upper shaft, a lock mechanism for releasably fastening the upper shaft to the lower shaft at its adjusted position, and stopper means for restricting downward movement of the upper shaft over a predetermined stroke during adjustment of the shaft assembly. Such stopper means includes, in general, a pair of stopper elements which are arranged respectively integral with the upper and lower shafts to be abutted at a predetermined position. In adjustment of the steering shaft assembly, it has been experienced that when the upper shaft is moved to its downward stroke end, the steering wheel is applied with an impact caused by abutment of the stopper elements. Even if in the shaft assembly a single shock absorber element of elastic material was interposed between the stopper elements to absorb the impact acting on the steering wheel, sufficient effect would not be expected because the magnitude of such impact changes in dependence upon the downward movement speed of the upper shaft. For example, if such a shock absorber element was made of soft elastic material, it would be effective to absorb a relatively small impact but ineffective to absorb a large impact. Alternatively, if such a shock absorber element was made of hard elastic material, it would be effective to absorb a large impact but ineffective to absorb a relatively small impact.